US liquefied natural gas company Cheniere Energy said on Friday (Saturday AEST) it had signed a 25-year deal to supply Taiwan's CPC Corp, which CPC valued at roughly $US25 billion ($34 billion).

Cheniere said it will sell two million tonnes of LNG per year on a delivered basis to the state-owned oil and gas company, starting in 2021. It said the purchase price will be pegged to the Henry Hub monthly average, plus a fee.

A CPC spokesman said the $US25 billion figure was based on current prices.

The deal is viewed as an important part of Taiwan's efforts to diversify its energy resources and reduce its trade surplus with the United States, according to a source familiar with the government's thinking.

The contract is a significant boost to Taiwan's trade relations with the US, particularly given the Trump administration's focus on trade with Asia, the source said.

The CPC deal, which is through Cheniere's marketing arm, is not tied to a particular project or liquefaction train.

Cheniere said the agreement ties up a portion of its portfolio volume on a long-term basis with a investment grade counterparty. The company also retains the ability to use those volumes to support a future train or expansion project.

Cheniere announced in May that it was moving ahead with a third liquefaction train at its Corpus Christi project. It is currently marketing its sixth train at Sabine Pass, with an investment decision expected next year.

Taiwan is the world's fifth biggest importer of LNG, shipping in almost 16.8 million tonnes in 2017, according to the International Gas Union, giving the island a global import market share of almost 6 per cent. (